I can't speak for a React test specifically, but I've seen developers work through thought experiments. The interviewer will ask if how you'd debug a certain issue, and have you walk him through your process. They want to see what you do, like checking the DevTools / console, or if you have the skill to Google the right issue.
For a React-centric interview, I'd expect some questions like:
Basically anything you'd find in the React docs and Dan Abramovs twitter.
I'd also expect some questions about associated libraries or dependencies, like Redux or Flow. If you get questions about super specific stuff like Styled Components, they ask at that point to see how comfortable you are with their toolset -- it won't impede on your ability to get the job, just gets extra brownie points if ya know it.
You can find a Github repo here with sample React interview questions:
- How does React work?
- What are the advantages of using React?
- What is the difference between a Presentational component and a Container component?
- What are the differences between a class component and functional component?
- What is the difference between state and props?
- Name the different lifecycle methods?
- Where in a React component should you make an AJAX request?
- What are controlled components?
- What are refs used for in React?
- What is a higher order component?
- What advantages are there in using arrow functions?
- Why is it advised to pass a callback function to setState as opposed to an object?
- What is the alternative of binding this in the constructor?
- How would you prevent a component from rendering?
- When rendering a list what is a key and what is its purpose?
- What is the purpose of super(props)?
- What is JSX?
- What is equivalent of the following using React.createElement?
- What is Children?
- What is state in react?
- Why would you eject from create-react-app?
- What is redux?
- What is a store in redux?
- What is an action?
- What is a reducer?
- What is redux thunk used for?
- What is a pure function?
- What do you like about React?
- What don't you like about React?
Hope that helps! 👍